Tailored Properties By Post Hot Forming Processing

ABSTRACT

A method of forming a product from an initial blank comprises subjecting the initial blank to a hot forming and press hardening operation to form the product with substantially a uniform first tensile strength. Subsequently, the product is subjected to post hot-forming processing in which a first region of the product is heated selectively to above a known temperature, using one of conduction heating, resistance heating, and induction heating. The first region is then cooled, such that the first region attains a second tensile strength that is substantially less than the first tensile strength.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Ser.No. 61/358,174 filed Jun. 24, 2010, the entire disclosure of theapplication being considered part of the disclosure of this application,and hereby incorporated by reference.

FIELD OF THE INVENTION

The instant invention relates generally to metallic products havingtailored properties, and more particularly to a method of producingregions of reduced hardness and reduced strength in products via posthot-forming processing.

BACKGROUND OF THE INVENTION

In the field of vehicle construction, more and more vehicle parts thatare made of high-strength and ultra-high-strength steel are beingemployed in order to satisfy criteria for lightweight construction. Thisapplies to car body construction where, in order to meet weight goalsand safety requirements, for instance structural and/or safety elementssuch as door intrusion beams, A and B columns, bumpers, side rails andcross rails are increasingly being produced from UHSS (Ultra HighStrength Steel), thermo-shaped and press-hardened steel having tensilestrengths greater than 1000 MPa.

In different applications of motor vehicle engineering, shaped parts areto have high strength in certain regions while in other regions they areto have higher ductility relative thereto. “Tailoring” the properties ofshaped parts in this way facilitates subsequent forming operations, suchas for instance trimming or perforating the part, and results in regionsthat can convert crash energy into deformation by crumpling.

It is known to treat a part using heat treatments such that localregions have higher strength or higher ductility. Lundstrom disclosesone such approach in U.S. Pat. No. 5,916,389, wherein a sheet ofhardenable steel is heated to an austenitization temperature and thenpressed between cooled die halves in order to form a shaped part havinga desired profile. Sections of the die halves that are adjacent toportions of the part that are to have higher ductility in the finishedproduct are adapted to prevent rapid cooling, such that hardening doesnot occur within these portions to the same extent that it occurs withinother portions of the finished product. Unfortunately, the die halvesmust be specially made for each part, which is both laborious andcostly. In addition, special effort is required in order to minimize theextent of formation of transition regions between the differentportions, since typically these transition regions exhibit propertiesthat are less well defined than the properties of the rest of thefinished product.

In another approach, a shaped product having substantially uniformhardness is produced using conventional hot forming and press hardeningtechniques, followed by separate additional heat treatment processing ofthe product to form regions of lower tensile strength therein. Forinstance, in United States patent application Publication 2010/0086803,Patberg discloses a method of forming mild zones along a bend edge of ahot formed and press hardened component. In particular, a laser beam isused to heat a narrow region of the component along the bend edge.Additionally, Patberg suggests that the heat that is produced by weldingmay result in the formation of mild zones adjacent to a weld joint.Unfortunately, the use of highly specialized laser equipment adds to thecost and complexity of manufacturing the component. In addition, thisapproach is not well suited either to batch processing or toapplications requiring the formation of substantial regions havingreduced tensile strength within the component.

It would be advantageous to provide a method that overcomes at leastsome of the above-mentioned limitations of the prior art.

SUMMARY OF EMBODIMENTS OF THE INVENTION

According to at least one embodiment of the instant invention, a methodof forming a product from an initial blank is provided in which theinitial blank is subjected firstly to a hot forming and press hardeningoperation, so as to form the product with substantially a uniform firsttensile strength. In particular, the initial blank is heated to atemperature above its transition temperature Ac3, which is defined asthe temperature at which transformation of ferrite into austenite iscompleted upon heating. By way of a specific and non-limiting example,the initial blank is heated to approximately 950° C. The heated initialblank is inserted into a cooled press having a pair of die halves, whichis used for both hot forming and hardening the product. The press issubsequently closed, thereby deforming the initial blank such that itconforms to contours that are defined along facing surfaces of the diehalves. Deformation and concomitant rapid cooling of the initial blankwithin the die halves produces the product, in which the austenitestructure has been transformed into martensite structure. The tensilestrength and hardness of the product is substantially uniformthroughout. Optionally, the die halves are not cooled, provided that asuitably rapid cooling rate of the product can still be achieved to formthe martensite structure.

Subsequently, in a second thermal treatment step, a first region of theproduct is heated in a selective fashion to a known temperature that islower than the transition temperature Ac3. By way of a specific andnon-limiting example, the first region of the product is heated to atemperature between approximately 370° C. and 800° C. In an embodiment,the first region of the product is heated to a temperature within therange of temperatures between about 400° C. and 700° C. By way ofseveral specific and non-limiting examples, the first region of theproduct is heated using one of conduction heating, resistance heating,and induction heating. The first region is then cooled in such a waythat the first region attains a second tensile strength that issubstantially less than the first tensile strength. The second thermaltreatment at a temperature between approximately 370° C. and 800° C.results in a tempered martensite composition within the first region.

Optionally, the conduction heating may be performed using heatingplates, such as for instance a heated die, or using a heated fluid and asuitable contacting medium, such as for instance hot compressed air andone of sand, ceramic, salt, etc. Optionally, the induction heating isperformed using one or more induction coils, or alternatively theinduction heating is performed using induction plates.

According to an embodiment of the instant invention, the first region ofthe product is gas-cooled subsequent to the second thermal treatmentstep. Optionally, the first region of the product is cooled usinganother suitable cooling technique, such as for instance one ofgas-blasting, fluidized bed cooling, die cooling, water/mist cooling,and cooling with the use of cooling fans/jets.

According to an embodiment, other regions of the product are cooled orat least insulated from being heated to the known temperature as aresult of the one of conduction heating, resistance heating andinduction heating. For instance, the product is gripped using a cooledcollar that surrounds a second region of the product that is adjacent tothe first region. Alternatively, the second region of the product isprotected from being heated using a curtain of a cooled gas, such as forinstance air, or by spraying or misting the second region with asuitable cooling liquid, such as for instance water.

Intermediate processing, such as for instance forming and/or cuttingand/or perforating, etc., optionally is performed subsequent to the hotstamping and press hardening steps but prior to the post hot-formingprocessing. Optionally, forming and/or cutting and/or perforating, etc.is performed subsequent to the post hot-forming processing.

According to another embodiment of the instant invention, the hotforming and press hardening steps are omitted. By way of a specific andnon-limiting example, the product is roll formed from a coil of UltraHigh Strength Steel and subjected subsequently to post-forming thermaltreatment by the one of conduction heating, resistance heating andinduction heating as described above. In particular, products may beformed having a geometry that is not sufficiently complex so as torequire the use of hot forming and press hardening techniques.

Optionally, the initial blank is formed from either a coated material oran uncoated material.

In accordance with an aspect of an embodiment of the invention there isprovided a method of forming a product from an initial blank,comprising: subjecting the initial blank to a hot forming and presshardening operation to form the product with substantially a uniformfirst tensile strength; and subsequently, subjecting the product to posthot-forming processing, comprising selectively heating a first region ofthe product to above a known temperature, while simultaneouslymaintaining below the known temperature a second region of the productthat is adjacent to the first region, and then cooling the first regionsuch that the first region attains a second tensile strength that issubstantially less than the first tensile strength.

In accordance with an aspect of an embodiment of the invention there isprovided a method of forming a product from an initial blank,comprising: heating the initial blank to an austenitizing temperature;hot-shaping the initial blank in a cooled pair of dies to form theproduct; cooling the product during a first period of time, using a rateof cooling that is sufficiently rapid to support formation of amartensitic structure within substantially the entire product;subjecting a first portion of the product to post hot-formingprocessing, comprising selectively heating the first portion of theproduct to a known temperature that is less than the austenitizingtemperature, while simultaneously maintaining below the knowntemperature a second portion of the product that is adjacent to thefirst portion; and, cooling the product such that tempered martensite isformed within the first portion of the product while at the same timethe second portion of the product remains substantially free of temperedmartensite.

In accordance with an aspect of an embodiment of the invention there isprovided a method of forming a product from an initial blank,comprising: providing the initial blank; heating the initial blank tothe austenite state; hot-shaping the initial blank in a cooled pair ofdies to form the product; hardening substantially the entire productwhile it is still inside the pair of dies by cooling the product using arate of cooling that is sufficiently fast to form a martensiticstructure; using conduction heating, heating a first portion of theproduct to at least a predetermined first temperature, while at the sametime maintaining a second portion of the product below a predeterminedsecond temperature that is lower than the first temperature; and,cooling the product such that tempered martensite is formed within thefirst portion of the product while at the same time the second portionof the product remains substantially free of tempered martensite,wherein subsequent to cooling, a tensile strength of the first portionof the product is less than a tensile strength of the second portion ofthe product.

In accordance with an aspect of an embodiment of the invention there isprovided a method of forming a product from an initial blank,comprising: providing the initial blank; heating the initial blank tothe austenite state; hot-shaping the initial blank in a cooled pair ofdies to form the product; hardening substantially the entire productwhile it is still inside the pair of dies by cooling the product using arate of cooling that is sufficiently fast to form a martensiticstructure; using resistance heating, heating a first portion of theproduct to at least a predetermined first temperature, while at the sametime maintaining a second portion of the product below a predeterminedsecond temperature that is lower than the first temperature; and,cooling the product such that tempered martensite is formed within thefirst portion of the product while at the same time the second portionof the product remains substantially free of tempered martensite,wherein subsequent to cooling, a tensile strength of the first portionof the product is less than a tensile strength of the second portion ofthe product.

In accordance with an aspect of an embodiment of the invention there isprovided a method of forming a product from an initial blank,comprising: providing the initial blank; heating the initial blank tothe austenite state; hot-shaping the initial blank in a cooled pair ofdies to form the product; hardening substantially the entire productwhile it is still inside the pair of dies by cooling the product using arate of cooling that is sufficiently fast to form a martensiticstructure; using induction heating, heating a first portion of theproduct to at least a predetermined first temperature, while at the sametime maintaining a second portion of the product below a predeterminedsecond temperature that is lower than the first temperature; and,cooling the product such that tempered martensite is formed within thefirst portion of the product while at the same time the second portionof the product remains substantially free of tempered martensite,wherein subsequent to cooling, a tensile strength of the first portionof the product is less than a tensile strength of the second portion ofthe product.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described inconjunction with the following drawings, in which:

FIG. 1 is a schematic diagram of a thermoforming line for a steelcomponent, including post hot-forming processing, according to anembodiment of the instant invention;

FIG. 2 is a top view depicting a B column having substantially uniformtensile strength, as formed by a conventional hot forming process;

FIG. 3 is a top view depicting the B column of FIG. 2, with a firstregion thereof being subjected to post hot-forming processing, accordingto an embodiment of the instant invention;

FIG. 4 is a top view depicting the B column of FIG. 2, havingsubstantially two regions of different tensile strength due to posthot-forming processing, according to an embodiment of the instantinvention;

FIG. 5 a is a simplified side view of a system for post hot-formingprocessing by conduction heating using heated plates, according to anembodiment of the instant invention;

FIG. 5 b is a simplified diagram depicting a first region of a productdisposed between the pair of conduction heating plates of FIG. 5 a;

FIG. 6 a is a simplified perspective view showing a product beingsubjected to conduction heating using a heated fluid and a suitablecontacting medium, according to an embodiment of the instant invention;

FIG. 6 b is a partial cut-away view showing the product being subjectedto conduction heating by the heated fluid and the suitable contactingmedium of FIG. 6 a;

FIG. 7 is a simplified diagram showing a first region of a product beingsubjected to resistance heating, according to an embodiment of theinstant invention;

FIG. 8 a is a simplified diagram showing a product being subjected toinduction heating using coils that are disposed along opposite sides ofa first region of the product, according to an embodiment of the instantinvention;

FIG. 8 b is a simplified diagram showing a product being subjected toinduction heating using a coil that encircles a first region of theproduct, according to an embodiment of the instant invention;

FIG. 9 a is a simplified perspective view showing a first region of aproduct being subjected to induction heating using induction plates,according to an embodiment of the instant invention;

FIG. 9 b is a simplified side view showing the product of FIG. 9 a beingsubjected to induction heating using induction plates, according to anembodiment of the instant invention;

FIG. 10 is a simplified flow diagram of a method according to anembodiment of the instant invention;

FIG. 11 is a simplified flow diagram of another method according to anembodiment of the instant invention; and

FIG. 12 is a simplified flow diagram of yet another method according toan embodiment of the instant invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The following description is presented to enable a person skilled in theart to make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the scope ofthe invention. Thus, the present invention is not intended to be limitedto the embodiments disclosed, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

Referring to FIG. 1, shown is a schematic diagram of a thermoformingline for a steel component, according to an embodiment of the instantinvention. By way of a specific and non-limiting example, the componentthat is produced in FIG. 1 is a B column for an automobile. Of course,other types of components may be produced in a similar fashion, and thespecific example of the B column is provided merely for illustrativepurposes and in order to facilitate a better understanding of theembodiments of the instant invention.

An initial blank 100 is provided. For instance, the initial blank 100 isstamped from a sheet of hardenable steel, such as Usibor® 1500P, Usibor®1500, another suitable boron steel or any suitable hot stamp presshardened material. Optionally, the initial blank 100 is pre-shapedspecifically for producing a B column, such as for instance by anadditional cutting step or an additional cold forming step (not shown inFIG. 1). The entire initial blank 100 is then heated in an oven 102 to atemperature above the Ac3 temperature. By way of a specific andnon-limiting example, the oven 102 is a roller-hearth or a batch styleoven. Once the initial blank 100 is in the austenite state it istransferred rapidly to a die set shown generally at 104, the die set 104having an upper die half 106 and a lower die half 108. The die set 104optionally is cooled in order to ensure that a sufficiently rapidcooling rate of the initial blank 100 is achieved, such that martensiteis formed. By way of a specific and non-limiting example, channels aredefined through the upper die half 106 and through the lower die half108 for flowing a cooling fluid, such as for instance water, oil,saline, etc., through the die halves to achieve the rapid cooling rateof the product that is being formed from the initial blank 100. Forinstance, a typical cooling rate is in the range of about 30° C./secondto about 100° C./second. The product is held inside the die set duringcooling, so as to maintain the desired shape of the product while it isbeing cooled and hardened. After being removed from the die set 104, theproduct (shown at 110) is further cooled to about room temperature, orat least to a temperature between about 20° C. and about 250° C. At thisstage, the product 110 has substantially a uniform martensite structure.

After the product 110 has cooled to the desired temperature, it issubjected to a post hot-forming process 112. The post hot-formingprocess 112 includes heating a first region 120 of the product 110,which is to have reduced tensile strength in the finished product (i.e.,“a soft zone”), to a known temperature. The known temperature is in therange between about 370° C. and about 800° C., and in particular betweenabout 400° C. and about 700° C.

Referring still to FIG. 1, the first region 120 of the product 110 isheated using one of conduction heating, resistance heating, andinduction heating. Heating by conduction heating is described in greaterdetail with reference to FIGS. 5 a, 5 b, 6 a and 6 b, heating byresistance heating is described in greater detail with reference to FIG.7, and heating by induction heating is described in greater detail withreference to FIGS. 8 a, 8 b, 9 a and 9 b. The first region 120 is heatedto the known temperature between about 370° C. and about 800° C., and inparticular between about 400° C. and about 700° C. Optionally, a secondregion 122 adjacent to the first region 120 is cooled and/or insulated,so as to prevent substantial heating of the second region 122 during thepost hot-forming processing. For instance, the second region 122, whichis to have high tensile strength in the finished product, is protectedfrom being heated using a curtain of cooled gas (such as for instancecooled air) or by spraying or misting with a cooling liquid (such as forinstance water).

At the end of the post hot-forming processing, the first region 120 ofthe product 110 is cooled to room temperature. According to oneembodiment of the instant invention, the first region 120 is gas-cooled.Optionally, a fixture is used to maintain the dimensions of the product110 during the cooling process. Further optionally, the first region 120is cooled using another suitable cooling technique, such as for instanceone of gas-blasting, fluidized bed cooling, die cooling, water/mistcooling, and cooling with the use of cooling fans/jets, etc. Optionally,additional not illustrated post processing is performed subsequent tocooling, such as for instance trimming or perforating, etc. Optionally,the additional not illustrated post processing is performed subsequentto the hot forming and press hardening steps, but prior to the posthot-forming processing.

The post hot-forming processing results in the formation of temperedmartensite within the first region 120 of the product 110, due to themetal within that region being reheated to between about 370° C. andabout 800° C. and then cooled. On the other hand, the second region 122of the product 110 is not reheated and cooled in this way, such thattempered martensite is not formed within the second region 122. Instead,the original martensite structure that is formed during the hot formingand press hardening operation is retained within the second region 122in the finished product. Of course, a transition zone (not illustrated)of finite width exists along the “boundary” 124 between the first region120 and the second region 122. The tensile strength of the product 110within the transition zone is intermediate the tensile strength withinthe first region 120 and the tensile strength within the second region122.

Optionally, additional cycles of heating the product 110, followed bycooling the product 110, are performed in order to form additional “softzones” within different regions of the product 110. Alternatively, twoor more non-contiguous regions of the product 110 are heated at the sametime, such that two or more “soft zones” are formed in a single pass.

Referring now to FIG. 2, shown is the product 110 that is obtained atpoint “A” of the thermoforming line of FIG. 1. The product 110 at point“A” is substantially uniformly of martensite structure. Referring now toFIG. 3, shown is the product 110 corresponding to point “B” of thethermoforming line of FIG. 1. The structure of the product 110 at point“B” is also substantially uniformly of martensite structure, but thefirst region 120 of the product 110 is being subjected to posthot-forming processing. FIG. 4 illustrates that two regions ofsubstantially different tensile strength are obtained at point “C” ofthe thermoforming line of FIG. 1, following the completion of posthot-forming processing of the product 110. More particularly, subsequentto being reheated and then cooled to room temperature, the second region122 on one side of boundary 124 retains the original martensitestructure, whereas tempered martensite has been formed within the firstregion 120 on the other side of the boundary 124. As discussed supra atransition zone (not illustrated) of finite width exists along the“boundary” 124 between the first region 120 and the second region 122.

The first region 120 of the product 110 may be heated by one ofconduction heating, resistance heating, and induction heating. Eachheating method will now be described in greater detail, below.

Referring to FIG. 5 a, shown is a simplified side view of a system 500for post hot-forming processing by conduction heating using heatedplates. The system 500 comprises a press 502 having an upper heatedplate 504 and a lower heated plate 506. A product 508 that is to besubjected to post hot-forming processing is positioned in the press,such that a first region thereof is disposed between the upper heatedplate 504 and the lower heated plate 506. This positioning isillustrated more clearly in FIG. 5 b, which shows a first region 508 aof the product 508 disposed in a stacked-arrangement between the upperand lower heated plates 504 and 506. A second region 508 b, which isadjacent to the first region 508 a, is positioned externally withrespect to the heated plates 504/506.

An actuator, for instance a hydraulic cylinder 510, moves the upperheated plate into and out of contact with the first region 508 a of theproduct 508, and additionally applies sufficient pressure to ensureconduction of heat from the upper and lower heated plates 504 and 506into the first region 508 a of the product 508. Optionally, the firstregion 508 a is soaked for a predetermined amount of time after itreaches a desired temperature, prior to the upper heated plate 504 beingwithdrawn by the action of the actuator 510. Further optionally, thesystem 500 includes a not illustrated cooling sub-system, which preventssubstantial heating of the second region 508 b of the product 508.

The upper and lower heated plates 504 and 506 are fabricated from asuitable, thermally conductive material, such as for instance copper.Although FIGS. 5 a and 5 b show a product 508 with a substantially flatsecond region 508 b disposed between flat upper and lower heated plates504 and 506, it is to be understood that optionally the upper and lowerheated plates 504 and 506 are shaped with contours matching any contoursof the second region 508 b of the product 508. In other words, the upperand lower heated plates 504 and 506 may be upper and lower die halvesthat are similar to the upper die half 106 and a lower die half 108,respectively, used to hot form and press harden the product 110 asdescribed with reference to FIG. 1.

In order to provide improved clarity, FIG. 5 a does not show a powersource or electrical wiring extending between the power source and theupper and lower heated plates 504 and 506. Additionally, suitabletemperature controllers and/or temperature sensors have been omittedfrom FIG. 5 a. Of course, numerous modifications of the system that isshown in FIG. 5 a may be envisaged, such as for instance replacing thehydraulic actuator 510 with another type of actuator, or moving thelower heated plate 506 instead of or in addition to moving the upperheated plate 504, etc.

Referring now to FIG. 6 a, shown is a simplified perspective view of aproduct 600 that is being subjected to conduction heating using a heatedfluid and a suitable contacting medium 602. The product 600 is partiallyimmersed in the heated fluid/contacting medium 602, which is containedwithin a containing vessel 604. The fluid may be a gas, such as forinstance hot compressed air, and the contacting medium may be anysuitable particulate such as for instance sand, ceramic or salt. By wayof a specific and non-limiting example, the heated fluid/contactingmedium 602 is set to a desired temperature between about 370° C. andabout 800° C., and in particular in the range of between about 400° C.and about 700° C.

FIG. 6 b is a partial cut away view showing the product 600 beingsubjected to conduction heating using the heated fluid/contacting medium602 of FIG. 6 a. In particular, a first region 600 a of the product 600is immersed in the heated fluid/contacting medium 602. The first region600 a of the product 600 is left immersed in the heated fluid/contactingmedium 602 until the first region 600 a reaches the desired temperaturein the range of between about 370° C. to about 800° C., and may or maynot be soaked at that temperature for a period of time. Optionally, asecond region 600 b of the product 600 is protected from being heated,for instance using a collar box that is arranged around the secondregion 600 b for cooling/insulating the second region. Optionally, thesecond region 600 b is protected from being heated using a curtain ofcooled gas (such as for instance cooled air) or by spraying or mistingwith a cooling liquid (such as for instance water).

The product 600 is subsequently removed from the heated fluid/contactingmedium 602, and the product 600 is cooled to room temperature. Accordingto one embodiment of the instant invention, the first region 600 a isgas-cooled. Optionally, a fixture is used to maintain the dimensions ofthe product 600 during the cooling process. Further optionally, thefirst region 600 a is cooled using another suitable cooling technique,such as for instance one of gas-blasting, fluidized bed cooling, diecooling, water/mist cooling, and cooling with the use of coolingfans/jets, etc.

In order to provide improved clarity, FIGS. 6 a and 6 b do not show aninlet or an outlet of the containing vessel 604, which are used when aflow of the heated fluid is being provided through the containing vessel604. Additionally, suitable temperature controllers, temperaturesensors, compressed air sources, etc. have been omitted from FIGS. 6 aand 6 b.

Optionally, the post hot-forming processing is performed usingconduction heating in which the product is contacted with hot oil or hotgas, or another suitable solid or fluid medium for transferring heatselectively to the first region that is to become a “soft zone” in thefinal product. Optionally, the post hot-forming processing is performedusing conduction heating in which the product is contacted with one ormore of a flame, plasma, microwave radiation, infrared radiation, etc.

Referring now to FIG. 7, shown is a simplified diagram of a product 700being subjected to post hot-forming processing, in which resistanceheating is used to heat a first region 700 a of the product 700. A powersource 702 is electrically coupled to the first region 700 a of theproduct 700 via contacts 704 a and 704 b and conductors 706 a and 706 b.In the example that is shown in FIG. 7, the contacts 704 a and 704 b areelectrically conductive clamps.

During use, electrical current is passed through the first region 700 aof the product 700 (as illustrated using dashed arrows in FIG. 7),thereby heating the first region 700 a of the product 700 to a desiredtemperature. By way of a specific and non-limiting example, the firstregion 700 a is heated to a desired temperature between about 370° C.and about 800° C., and in particular in the range of between about 400°C. and about 700° C. Optionally, the second region 700 b is protectedfrom being heated, such as for instance by using a curtain of cooled gas(e.g., cooled air) or by spraying or misting with a cooling liquid(i.e., water).

Referring now to FIGS. 8 a and 8 b, shown are simplified diagrams of aproduct 800 being subjected to post hot-forming processing, in whichinduction heating is used to heat a first portion 800 a of the product800. FIGS. 9 a and 9 b are simplified diagrams of a product 900 beingsubjected to post hot-forming processing, in which induction heating isused to heat a first portion 900 a of the product 900.

In general, induction heating is the process of heating an electricallyconducting object by electromagnetic induction, where eddy currents aregenerated within the object and resistance leads to Joule heating.Induction heating can produce high power densities, which allow shortinteraction times to reach the desired temperature. This gives tightcontrol of the heating pattern, with the pattern following the appliedmagnetic field quite closely and allows reduced thermal distortion anddamage. The depth of induction heating can be controlled through thechoice of induction-frequency, power-density, and interaction time.

Referring now specifically to FIG. 8 a, a system is shown for heatingthe first portion 800 a of the product 800 by induction heating using apair of induction coils 802 and 804. The induction coils 802 and 804 aredisposed, one each, along opposite sides of the first portion 800 a ofthe product 800.

Referring now to FIG. 8 b, a system is shown for heating the firstportion 800 a of the product 800 by induction heating using a singleinduction coil 806. As is shown in FIG. 8 b, the induction coil 806encircles the first portion 800 a of the product 800.

Referring now to FIG. 9 a, a system is shown for heating the firstportion 900 a of the product 900 by induction heating using inductionplates 904 and 906.

FIG. 9 b is a simplified side view showing the first portion 900 a ofthe product 900 being heated by induction heating using the inductionplates 904 and 906 of the system of FIG. 9 a.

Referring now to FIG. 10, shown is a simplified flow diagram of a methodaccording to an embodiment of the instant invention. At 1000 an initialblank is subjected to a hot forming and press hardening operation toform a product with substantially a uniform first tensile strength. At1002 the product is subjected to post hot-forming processing. The posthot-forming processing includes selectively heating a first region ofthe product to above a known temperature, while simultaneouslymaintaining below the known temperature a second region of the productthat is adjacent to the first region, and then cooling the first regionsuch that the first region attains a second tensile strength that issubstantially less than the first tensile strength.

Referring now to 11, shown is a simplified flow diagram of a methodaccording to an embodiment of the instant invention. At 1100 the initialblank is heated to an austenitizing temperature. At 1102 the initialblank is hot-shaped in a cooled pair of dies to form the product. At1104 the product is cooled during a first period of time, using a rateof cooling that is sufficiently rapid to support formation of amartensitic structure within substantially the entire product. At 1106 afirst portion of the product is subjected to post hot-formingprocessing, comprising selectively heating the first portion of theproduct to a known temperature that is less than the austenitizingtemperature, while simultaneously maintaining below the knowntemperature a second portion of the product that is adjacent to thefirst portion. At 1108 the product is cooled such that temperedmartensite is formed within the first portion of the product while atthe same time the second portion of the product remains substantiallyfree of tempered martensite.

Referring now to FIG. 12, shown is a simplified flow diagram of a methodaccording to an embodiment of the instant invention. The initial blankis provided at 1200. At 1202 the initial blank is heated to theaustenite state. At 1204 the initial blank is hot-shaped in a cooledpair of dies so as to form the product. At 1206 the entire product ishardened, while it is still inside the pair of dies, by cooling theproduct using a rate of cooling that is sufficiently fast to form amartensitic structure. At 1208 one of conduction heating, resistanceheating and induction heating is used to heat a first portion of theproduct to at least a predetermined first temperature, while at the sametime maintaining a second portion of the product below a predeterminedsecond temperature that is lower than the first temperature. At 1210 theproduct is cooled such that tempered martensite is formed within thefirst portion of the product while at the same time the second portionof the product remains substantially free of tempered martensite. In aproduct that is formed according to the method that is described withreference to FIG. 12, a tensile strength of the first portion of theproduct is less than a tensile strength of the second portion of theproduct.

Numerous other embodiments may be envisaged without departing from thescope of the instant invention.

1. A method of forming a product from an initial blank, comprising:subjecting the initial blank to a hot forming and press hardeningoperation to form the product with substantially a uniform first tensilestrength; and subsequently, subjecting the product to post hot-formingprocessing, comprising selectively heating a first region of the productto above a known temperature, while simultaneously maintaining below theknown temperature a second region of the product that is adjacent to thefirst region, and then cooling the first region such that the firstregion attains a second tensile strength that is substantially less thanthe first tensile strength.
 2. A method according to claim 1, whereinthe post hot-forming processing comprises using conduction heating toheat the first region of the product to above the known temperature. 3.A method according to claim 2, wherein the conduction heating isperformed using a heated die including at least one of an upper heateddie half and a lower heated die half.
 4. A method according to claim 2,wherein the conduction heating is performed using at least one heatedplate.
 5. A method according to claim 2, wherein the conduction heatingis performed using a heated fluid.
 6. A method according to claim 2,wherein the conduction heating is performed using a heated fluid and acontacting medium.
 7. A method according to claim 6, wherein thecontacting medium is selected from the group consisting of sand, saltand ceramic.
 8. A method according to claim 1, wherein the posthot-forming processing comprises using resistance heating to heat thefirst region of the product to above the known temperature.
 9. A methodaccording to claim 1, wherein the post hot-forming processing comprisesusing induction heating to heat the first region of the product to abovethe known temperature.
 10. A method according to claim 9, wherein theinduction heating is performed using a pair of induction coils disposedone each along opposite sides of the first region.
 11. A methodaccording to claim 9, wherein the induction heating is performed using asingle induction coil.
 12. A method according to claim 9, wherein theinduction heating is performed using a pair of induction plates disposedone each along opposite sides of the first region.
 13. A methodaccording to claim 1, wherein the initial blank is heated to anaustenitization temperature during the hot forming and press hardeningoperation, and wherein the known temperature is substantially lower thanthe austenitization temperature.
 14. A method according to claim 1,comprising protecting the second region from being heated tosubstantially the known temperature.
 15. A method according to claim 1,wherein the known temperature is between approximately 370° C. andapproximately 800° C.
 16. A method according to claim 1, wherein theknown temperature is between approximately 400° C. and approximately700° C.
 17. A method according to claim 1, wherein the initial blank isfabricated from a press hardenable steel alloy material.
 18. A method offorming a product from an initial blank, comprising: heating the initialblank to an austenitizing temperature; hot-shaping the initial blank ina cooled pair of dies to form the product; cooling the product during afirst period of time, using a rate of cooling that is sufficiently rapidto support formation of a martensitic structure within substantially theentire product; subjecting a first portion of the product to posthot-forming processing, comprising selectively heating the first portionof the product to a known temperature that is less than theaustenitizing temperature, while simultaneously maintaining below theknown temperature a second portion of the product that is adjacent tothe first portion; and, cooling the product such that temperedmartensite is formed within the first portion of the product while atthe same time the second portion of the product remains substantiallyfree of tempered martensite.
 19. A method of forming a product from aninitial blank, comprising: providing the initial blank; heating theinitial blank to the austenite state; hot-stamping the initial blank ina cooled pair of dies to form the product; hardening substantially theentire product while it is still inside the pair of dies by cooling theproduct using a rate of cooling that is sufficiently fast to form amartensitic structure; using conduction heating, heating a first portionof the product to at least a predetermined first temperature, while atthe same time maintaining a second portion of the product below apredetermined second temperature that is lower than the firsttemperature; and, cooling the product such that tempered martensite isformed within the first portion of the product while at the same timethe second portion of the product remains substantially free of temperedmartensite, wherein subsequent to cooling, a tensile strength of thefirst portion of the product is less than a tensile strength of thesecond portion of the product.
 20. A method of forming a product from aninitial blank, comprising: providing the initial blank; heating theinitial blank to the austenite state; hot-stamping the initial blank ina cooled pair of dies to form the product; hardening substantially theentire product while it is still inside the pair of dies by cooling theproduct using a rate of cooling that is sufficiently fast to form amartensitic structure; using resistance heating, heating a first portionof the product to at least a predetermined first temperature, while atthe same time maintaining a second portion of the product below apredetermined second temperature that is lower than the firsttemperature; and, cooling the product such that tempered martensite isformed within the first portion of the product while at the same timethe second portion of the product remains substantially free of temperedmartensite, wherein subsequent to cooling, a tensile strength of thefirst portion of the product is less than a tensile strength of thesecond portion of the product.
 21. A method of forming a product from aninitial blank, comprising: providing the initial blank; heating theinitial blank to the austenite state; hot-stamping the initial blank ina cooled pair of dies to form the product; hardening substantially theentire product while it is still inside the pair of dies by cooling theproduct using a rate of cooling that is sufficiently fast to form amartensitic structure; using induction heating, heating a first portionof the product to at least a predetermined first temperature, while atthe same time maintaining a second portion of the product below apredetermined second temperature that is lower than the firsttemperature; and, cooling the product such that tempered martensite isformed within the first portion of the product while at the same timethe second portion of the product remains substantially free of temperedmartensite, wherein subsequent to cooling, a tensile strength of thefirst portion of the product is less than a tensile strength of thesecond portion of the product.